Fire detector

Abstract

A fire detector with a maximum average response time of less than 1.5 minutes is obtained by combining a smoke detector with a CO 2 detector that uses NDIR sensor technology. The smoke detector is used to detect smoldering fires and to help prevent false alarms attributable to the CO 2 detector. The CO 2 detector is used to rapidly detect fires by measuring the rate of change of CO 2 concentration. A signal processor generates an alarm signal when a smoldering fire is detected or alarm logic indicates that a fire has been detected.

What is claimed is: 
     
       1. A fire detector that will detect smoldering fires and generate an alarm signal within a maximum average response time of approximately 1.5 minutes when subjected to Tests A-D described in paragraphs 42.3-42.6 of ANSI/UL 217-1985, Mar. 22, 1985, comprising: a photoelectric smoke detector that generates a smoke detector output signal representative of light obscuration;   a non-dispersive infrared gas sensor that generates an output signal representative of the rate of change of carbon dioxide (CO 2 ) concentration; and   a signal processor which receives the smoke detector output signal and the output signal of the NDIR gas sensor and generates the alarm signal when any of the following criteria is met: light obscuration exceeds a threshold level for longer than a first preselected time;   light obscuration exceeds a reduced threshold level and the rate of increase in the concentration of (CO 2 ) exceeds between approximately 150 to approximately 250 ppm/min; or   light obscuration exceeds a reduced threshold level for longer than a second preselected time.     
     
     
       2. A fire detector as recited in claim 1, wherein the signal processor will also trigger an alarm when the rate of increase in the concentration of CO 2  exceeds approximately 1000 ppm/min. 
     
     
       3. A fire detector as recited in claim 1, wherein the threshold level is approximately 7%, the reduced threshold level is substantially less than 7%, the first preselected time is approximately 5 minutes or more and the second preselected time is greater than the first preselected time but not greater than sixty minutes. 
     
     
       4. A fire detector as recited in claim 1, wherein a smoldering fire causes a smoldering fire alarm signal to be triggered whereas a non-smoldering fire causes a non-smoldering alarm signal to be triggered. 
     
     
       5. A method for decreasing a maximum response time of a fire detector for generating an alarm signal when the alarm signal is only generated when a smoke detector and a carbon dioxide (CO 2 ) detector generate an output indicative of a fire, comprising the step of generating the alarm signal when the rate of increase in the concentration of CO 2  detected by the CO 2  detector exceeds between approximately 150 to approximately 250 ppm/min. and light obscuration detected by the smoke detector exceeds a reduced threshold level. 
     
     
       6. A method as recited in claim 5, wherein the maximum average response time for the fire detector is less than approximately 1.5 minutes according to Tests A-D described in paragraphs 42.3-42.6 of ANSI/UL 217-1985, Mar. 22, 1985. 
     
     
       7. A method for generating an alarm signal in response to a fire, comprising the steps of: determining whether light obscuration exceeds a smoldering fire detection level for greater than a preselected time;   determining whether the rate of increase in the concentration of carbon dioxide (CO 2 ) exceeds a first predetermined rate; and   generating the alarm signal if light obscuration exceeds the smoldering fire detection level for greater than the preselected time or if light obscuration exceeds the reduced threshold level and the rate of increase in the concentration of CO 2  exceeds the first predetermined rate.   
     
     
       8. A method as recited in claim 7, comprising the further step of generating the alarm signal if the rate of increase in the concentration of CO 2  exceeds a second predetermined rate. 
     
     
       9. A fire detector, comprising: a smoke detector that generates a smoke detector output signal representative of light obscuration;   a carbon dioxide (CO 2 ) detector that generates an output signal representative of the rate of change of CO 2  concentration; and   a signal processor which receives the smoke detector output signal and the CO 2  detector output signal and generates an alarm signal when either of the following criteria is met: light obscuratation exceeds a smoldering fire detection level when light obscuration exceeds a reduced threshold level for greater than a second preselected time; or   light obscuration exceeds the reduced threshold level and the rate of increase in the concentration of CO 2  exceeds a first predetermined rate.     
     
     
       10. A fire detector as recited in claim 9, wherein the second preselected time is greater than five minutes but not greater than sixty minutes. 
     
     
       11. A fire detector as recited in claim 10, wherein the second preselected time is greater than five minutes but not greater than sixty minutes. 
     
     
       12. A fire detector, comprising: a smoke detector that generates a smoke detector output signal representative of light obscuration;   a carbon dioxide (CO 2 ) detector that generates an output signal representative of the rate of change of CO 2  concentration; and   a signal processor which receives the smoke detector output signal and the CO 2  detector output signal and generates an alarm signal when either of the following criteria is met: light obscuration exceeds a smoldering fire detection level when light obscuration exceeds a threshold level of approximately 7% for greater than a first preselected time of approximately 5 minutes or more or when light obscuration exceeds a reduced threshold level of substantially less than 7% for greater than a second preselected time which is greater than the first preselected time but not greater than sixty minutes; or   light obscuration exceeds the reduced threshold level and the rate of increase in the concentration of CO 2  exceeds a first predetermined rate.     
     
     
       13. A fire detector as recited in claim 12, wherein the signal processor will also trigger an alarm when the rate of increase in the concentration of CO 2  exceeds a second predetermined rate.